1. Field of the Invention
The present invention relates to an image processing apparatus, and more particularly to a judgement of a monochrome image and color image.
2. Description of the Prior Arts
Among printing systems such as printers are ones in which a process for a printing operation is automatically changed depending upon a fact that the inputted image is a monochrome image (gray image) or a color image. Specifically, the image is processed by monochrome processing in the case of the monochrome image, while the image is processed by color processing in the case of the color image. When a color image area is partially included in the monochrome image, this image is generally processed by a color image.
Japanese Published Unexamined Patent Application No. HEI 9-277606 discloses a conventional monochrome/color judging method. In this conventional method, it is judged to be a monochrome pixel if each of the color component values R, G and B (or C, M, Y and K) possessed by each pixel matches one another.
However, there is a case in the actual image data that each color component value possessed by a pixel does not match one another such as R=100, G=100 and B=101 due to a calculation error. Such a pixel is not visually recognized as a color pixel. If such a pixel is present, for example, as one pixel in one page or as one pixel in one job in the conventional method, the entire image is processed by color processing, thereby entailing a problem of ineffectiveness.
Japanese Published Unexamined Patent Application No. HEI 3-58176 discloses an automatic discriminating method of a monochrome/color document. In this method, a target pixel is judged to be a monochrome pixel or not from a balance of an original color signal (relative difference of a color component value), and then, the document is finally judged to be a color document or monochrome document by a number (ratio) of the monochrome pixels in the document. However, it is considered in this conventional method that the judging criterion of the monochrome pixel and color pixel is fixedly set, and further, man's visual characteristic is not considered. This disclosure discloses that the target pixel is compared with plural peripheral pixels for judging a uniformity of a density distribution.